Indium-gallium-zinc oxide (IGZO) devices, such as IGZO thin-film transistors (TFTs) have attracted a considerable amount of attention due to the associated low cost, room temperature manufacturing processes with good uniformity control, high mobility for high speed operation, and the compatibility with transparent, flexible, and light display applications. Due to these attributes, IGZO TFTs may even be favored over low cost amorphous silicon TFTs and relatively high mobility polycrystalline silicon TFT for display device applications. IGZO devices typically utilize amorphous IGZO (a-IGZO).
Recent developments in the field suggest that the use of crystalline IGZO may provide improved electrical and chemical stability in certain conditions. However, IGZO TFTs may lack electrical stability under negative bias illumination temperature stress (NBITS). A complete understanding of why this instability occurs in oxide semiconductors is crucial to prevent it from happening, and there have been many attempts to explain its origin, the major two arguments being the charge trapping model and the ion diffusion model. Recent reports support the charge trapping model, where holes generated in the IGZO layer upon illumination tunnel into traps in the gate dielectric when the gate electrode is negatively biased and cause a negative threshold shift.